Polyimides are used as dielectric layers in a variety of microelectronic applications, as they have good processability, low dielectric constant, high thermal stability, low moisture absorption, and good mechanical properties. Metal patterns are disposed on polyimide surfaces to form electrically conducting lines on chips and chip packages.
For example, in the formation of multilayer substrates for mounting chips, one configuration uses an insulating substrate of a ceramic material onto which is deposited a pattern of metallic conductors. Conventionally, the conductors are three layers of metal, including a layer of chromium, a layer of copper, and an overlying layer of chromium. A layer or film or a polyimide is placed on top of the metallized ceramic substrate, and a second layer of a pattern of conductors is placed on top of the metallized ceramic substrate. The metal contacting the polyimide on the second or subsequent layer can be copper, as disclosed in Nair et al. U.S. Pat. No. 4,386,116, assigned to International Business Machine Corporation, the entire disclosure of which is incorporated herein by reference.
However, direct adhesion of metals or polyimides to polyimide is weak. Failure to activate a polymeric surface will normally cause subsequent coatings to be poorly adhered and easily cracked, blistered, or otherwise removed. Surface treatments and adhesion layers have been used to enhance the adhesion of metal or polyimide layers to polyimides. These methods can introduce contamination, resulting in reliability failures. Modifying the polyimide chemically by introducing new foreign materials or new functional groups may cause reliability problems as well.
A number of methods have been used to improve adhesion of metals to polyimide surfaces. For example, Haines, in U.S. Pat. No. 3,445,264, discloses that the surfaces of polyimide articles can be treated to activate the surfaces and render them more adherent toward coating compositions by exposing the surface of the polymeric article to an activating solution consisting of alkaline metals, alkaline earth metals, hydrides, or amides of alkaline metals or alkaline earth metals in a dialkyl sulfoxide solvent vehicle.
Brandt et al., in U.S. Pat. No. 3,881,049, disclose that copper can be deposited onto a surface of a polyimide article by treating the polyimide surface with a solution of a noble metal salt and a halogenated alkanoic acid, and then drying the surface at an elevated temperature. The surface is then treated with a solution including a reducing agent, after which the surface is treated with a solution containing a copper salt and a reducing agent.
Grapentin et al, in U.S. Pat. No. 4,517,254, disclose a process for adhesive metallization of polyimide by pretreating the polyimide and subsequently activating the polyimide. The polyimide is pretreated with an aqueous solution of alkali hydroxide and an organic nitrogen compound such as N,N,N',N'-tetra-(2-hydroxypropyl)-ethylenediamine, ethylenediaminetetraacetic acid, and nitrilotriacetic acid.
Jobbins, in U.S. Pat. No. 4,528,245, discloses a process for conditioning the surfaces of polyimides and other polymers by exposing the surfaces to an atmosphere comprising ozone, contacting the surfaces with a conditioning solvent, and washing the surfaces with an aqueous solution of at least one surfactant. These polymers can then be electrolessly plated.
Manwiller et al., in U.S. Pat. No. 4,755,555, disclose a particulate polyimide molding resin which has a high surface area and low crystallinity. These polyimides are formed by reacting at least one organic diamine with at least one tetracarboxylic acid dianhydride to form a polyamide acid. This polyamide acid is then precipitated from solution and subsequently converted to a polyimide by heating. By carefully controlling the reaction parameters, a polyimide having high surface area and low degree of crystallinity is produced. These polyimides are particularly tough.
Fraenkel et al., in U.S. Pat. No. 4,803,097, disclose a process for conditioning the surfaces of plastic materials such as polyimides in order to facilitate electroless plating of the plastics. The surfaces of the plastic article are exposed to an ozone atmosphere, and then contacted with a conditioning solvent such as at least one alcohol and at least one strong base, and then contacted with an oxidizing agent. The surface is then ready for electroless deposit of a metal coating thereon.
Ouderkirk et al., in U.S. Pat. No. 4,822,451, disclose a method of rendering surfaces of semicrystalline polymers quasiamorphous by irradiation. This enhances the surfaces' ability to bond to other materials. The surface of these quasi-crystalline polymers can be amorphized by exposure to an intense short pulse UV excimer laser or short pulse duration, high intensity UV flashlamp. This procedure is useful primarily for polyethylene terephthalate, although it can be used for UV absorbing polymers such as nylon, other polyesters, poly(vinylchloride) with UV absorbing plasticizer.
Woo et al., in U.S. Pat. No. 4,824,699, disclose that coatings can be adhered directly to semicrystalline polymer films by first rendering the surface of the film quasi-amorphous, washing the surface with a solvent for amorphous polyester and coating the surface, or coating and heating the surface to a temperature to recrystallize the surface of the polymer. This process is particularly useful for polyethylene terephthalate.
Sirinyan et al., in U.S. Pat. No. 4,861,663, disclose that polyimides can be pretreated for subsequent surface coating by treating the polyimide surface with a solution of a mixture of salts comprising (a) halides of group I or II metals, particularly calcium chloride, magnesium chloride, lithium chloride, sodium chloride and/or potassium chloride; (b) salts of weak organic bases with strong inorganic acids, particularly aluminum chloride, ferric chloride, titanium tetrachloride, antimony pentachloride, calcium chloride, ferrous chloride, cupric chloride, zinc chloride and/or molybdenum chloride and/or the chelate complexes of these salts with Schiff bases, amines, carboxylic acids, diketones, .alpha.,.beta.-unsaturated ketones and phosphines; (c) in a non-corrosive, I5 organic swelling agent or solvent for the materials mentioned, where appropriate. With the addition of water, preferably in an alcohol, at temperatures up to the boiling point of the solvent, the molded articles are washed with water or other solvent and are then dried.
Anschel et al. in U.S. Pat. No. 4,931,310, disclose a method for treating the surface of polyimides to improve the properties of the polyimides. The surface of the polyimide is first treated with a base to convert the surface layer of the polyimide to polyamic acid, and the surface layer of the converted polyamic salt formed on the surface is treated with an acid to convert the layer of a polyamic acid, followed by a cure to prevent the formation of any significant amounts of transimide. The metal is then applied to the surface layer.
The major disadvantage of the above processes for treating polyimides is that adhesion layers or chemicals remain on the polyimide surface after pretreatment thereof.
It is yet another object of the present invention to provide a polyimide layer coated onto at least part of the surface of a crystalline polyimide body.